Perfil sísmico vertical

FIG. V-10. Vertical seismic profile. (a) Each trace is recorded at a depth in a borehole using an air-gun source at the surface. (b) Same except each trace has been shifted by the one-way traveltime to the surface, thus aligning reflections (upcoming events) horizontally. A shift in the other direction would align downgoing events horizontally. (c) Portion of a reflection record section across the well location. (d) Sonic log in the well.

Mediciones de la respuesta de un geófono en varias profundidades dentro de un pozo a partir de fuentes sobre la superficie. Ver Figuras V-10, V-11, y Sheriff y Geldart.

Sometimes the surface sources are moved about the area as well as the geophone depth being changed. Where the source point is an appreciable horizontal distance from the well head, the result is an offset VSP; this provides a way to look to the side of the borehole.

For an azimuthal VSP sources are offset in different directions. In a walkaway VSP a surface source moves while the geophone in the borehole remains stationary; this provides another way to look to the side of the borehole. In a reversed VSP the source is in the borehole and geophones are on the surface.

VSPs are also run in directional and horizontal wells. A walkabove VSP is made with the sonde in a deviated hole and the source moved so as to be vertically above it.

The result of a VSP is often displayed as a corridor stack; see Figure C-16.

FIG. V-11. Vertical seismic profile checklist.

FIG. C-16. Corridor stack. ‘‘Corridor stack’’ means the outer corridor unless ‘‘inner’’ precedes it. (1) Median-filtered VSP; (2) inside corridor; (3) inside-corridor stack; (4) outside-corridor stack; (5) outside corridor (reversed in direction).

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